Modification of the hydration characteristics of form ii sodium tripolyphosphate prior to detegent processing



United States Patent N 3,056,652 MUDiFECATlGN Gir THE HYDRATION CHARAC-TERlSTiCS 01 FORM ll SGDIUM TRWOLYPHOS- PHATE PRIOR TQ DETERGENTPRUQESSHNG Frederick V. Ryer, Oradeii, N.J., assignor to Lever BrothersCompany, New York, N.Y., a corporation of Maine No Drawing. Filed Nov.26, 1957, Ser. No. 698,911 3 Claims. (Cl. 23-106) The present inventionrelates to the treatment of Form II anhydrous sodium tripolyphosphate,and more particularly to a process for converting fast hydrating Form IIanhydrous sodium tripolyphosphate into slow hydrating Form 11 anhydroussodium tripolyphosphate.

Sodium tripolyphosphate, also called sodium triphosphate, is eitheranhydrous or hydrated and the anhydrous crystalline form may be eitherForm I or Form H, the anhydrous tripolyphosphate produced in the hightemperature regions being known as Form I, While the an hydroustripolyphosphate produced in the low temperature regions is known asForm II. The Form I variety hydrates quite rapidly, while the Form IIvariety hydrates at a much slower rate than the Form I variety. Thisproperty of rapid hydration causes lumping in aqueous slurries andaccordingly the soap and detergent industry has preferred to employ theForm II variety to avoid hydration as much as possible.

Detergent compositions containing tripolyphosphates have advantages overdetergent compositions containing other phosphates, such aspyrophosphates or orthophosphates. Repeat washing tests in hard waterindicate that clothes washed with detergent compositions containingtripolyphosphates have a lower ash content than clothes washed withdetergent compositions containing a pyrophosphate. A given weight of atripolyphosphate s questers more calcium from the Wash Water than does apyrophosphate, and hence clearer solutions are obtainable in hard waterswith detergent compositions containing tripolyphosphates than withdetergent compositions containing pyrophosphates.

Under the conditions for the preparation of detergent compositionscontaining Form If sodium tripolyphosphate in granulated, powdered orflake form, difliculty has been encountered due to the formation of thehexahydrate and subsequent thermal decomposition of the hexahydrate intoless desirable and sometimes objectionable pyrophosphates andorthophosphates. One undesirable result of such decomposition is a dropin the pH of solutions of theresulting product. The art has compensatedfor this result by adding additional alkaline material to thecomposition rather than by devising ways of avoiding the decomposition.Another adverse result of the decomposition is the release of freesilica by the reaction of the acid phosphate formed with the silicateusually present in such compositions. This free silica causes solutionsof the product to have a turbid, cloudy appearance which the consumerfinds unsightly. Also, when sodium tripolyphosphate becomes hydrated tothe hexahydrate, this causes troublesome viscosity changes, i.e., anincrease in viscosity, in a spray mix of the detergent composition bothin the crutcher and during the time between completion of the mixingoperation and the arrival of the mix at a spray nozzle. It is noted thatall these undesirable complications result from that portion of thetripolyphosphate which hydrated in the slurrying operation. Hence,minimizing the degree of hydration permitted can be expected to minimizethe undesirable side reactions.

Form II anhydrous sodium tripolyphosphate from different suppliers andfrom different lots from the same supplier or which have been exposed todifferent conditions Patented Oct. 2, 1962 in transit or in storage havemarkedly different rates of hydration upon addition to an aqueousmixture. These diifering hydration rates make it impossible to obtain auniform spray-dried detergent product without frequent adjustment of theprocessing conditions.

This tripolyphosphate may be graded into fast hydrating and slowhydrating types by the following test procedure. Preheat under runninghot tap water a Wide mouthed Dewar flask of approximately one pintcapacity, a four-bladed glass stirrer and a thermometer, and thenquickly assemble the apparatus so that the stirrer just clears thebottom of the flask and the thermometer bulb just clears the stirrerblades. Add 25 grams of anhydrous sodium sulfate and 100 cc. of boilingwater to the flask and start the stirrer motor. When the sodium sulfatesolution has cooled to 170 F., add grams of the Form II anhydrous sodiumtripolyphosphate to the flask and start a stopwatch. Record temperaturereadings of the slurry every minute for 15 minutes. By this testprocedure the slurry of the fast hydrating Form II anhydrous sodiumtripolyphosphate will thicken and the temperature will rise, forexample, from 170 F. to 186 F, while the slurry of the slow hydratingForm II anhydrous sodium tripolyphosphate will remain thin and thetemperature will fall, for example, from 170 F. to 152 F. after theoriginal heat of solution noted in the first minute. It has been foundthat the hydration characteristics as revealed by this test accuratelyforetell the behaviors in full detergent slurrying. Thus, the fasthydrating Form Il anhydrous sodium tripolyphosphate will hydrateextensively and lead to the undesirable complications noted above, Whilethe slow hydrating Form II anhydrous sodium tripolyphosphate willundergo only minimum hydration and side reactions.

In accordance with the present invention it was found that a fasthydrating Form II anhydrous sodium tripolyphosphate may be convertedinto a slow hydrating Form II anhydrous sodium tripolyphosphate byheating the fast hydrating Form II anhydrous sodium tripolyphosphate. Ingeneral, the temperature of heating may be from about C. to about 380C., the time of heating, of course, being less at the highertemperature. For example, conversion is obtained by heating the fasthydrating Form II anhydrous sodium tripolyphosphate for about six hoursor more at a temperature of about 100 C. or for about one hour or moreat a temperature of about 380 C.

The fundamental difierence between the fast and slow hydrating varietiesof Form II anhydrous sodium tripolyphosphate cannot be readilyestablished by wet chemical analyses, X-ray diffractograms, Form Icontent, or particle size determinations. While it will be appreciatedthat the invention is not to be limited by any theory expressed herein,it is believed that Form II anhydrous sodium tripolyphosphate exists inboth a fast hydrating and a slow hydrating variety because of smallvariations in adsorbed Water on the tripolyphosphate. Apparently, thefast hydrating Form II anhydrous sodium tripolyphosphate contains moreadsorbed water than the slow hydrating Form II anhydrous sodiumtripolyphosphate which adsorbed water catalyzes the rate of hydrationand the fast hydrating variety is therefore converted into a slowhydrating variety by heating the fast hydrating variety to therebyremove the adsorbed water.

By the process of the present invention, therefore, it is now possibleto produce a spray-dried detergent composition containing sodiumtripolyphosphate wherein an aqueous solution of the composition willshow only a minimum drop in pH compared with the aqueous crutcher slurryfrom which the spray-dried product is prepared. One is also now able toprovide a spray-dried detergent composition containing sodiumtripolyphosphate wherein an aqueous solution of the composition will notshow a large amount of Objectionable silica floc when the detergentcomposition contains a silicate as a component thereof. In addition, theprocess of the present invention makes possible the avoidance oftroublesome increases in viscosity in a spray mix of a tripolyphosphatedetergent composition both in the crutcher and during the time betweenthe completion or" the mixing operation and the arrival of the mix at aspray nozzle. These advantages result directly from preventingsubstantial hydration of the tripolyphosphate to the thermally unstablehexahydrate and its subsequent decomposition on spray-drying to acidicorthoand pyrophosphates.

The process of the present invention will be further illustrated by thefollowing examples which set forth not only the process of theinvention, but also demonstrate quite clearly the beneficial resultsflowing from the use thereof.

Example 1 A lot of Form II anhydrous sodium tripolyphosphate as receivedfrom the supplier was divided into two portions. 75 grams of one portionwas added to 100 cc. of water containing 25 grams of anhydrous sodiumsulfate and having a temperature of 170 F. in accordance with the abovetest procedure. During the next 15 minutes the slurry thickened and thetemperature thereof rose as shown below, thereby indicating that thetripolyphosphate was a fast hydrating variety.

Time (minutes): Temperature of slurry F.)

The second portion was heated in a tray for 17 hours at 110 C. and thencooled to room temperature. 75 grams of this heat-treated second portionwas added to 100 cc. of water containing 25 grams of anhydrous sodiumsulfate and having 'a temperature of 170 F. in accordance with the abovetest procedure. During the next 15 minutes the slurry remained thin andthe temperature thereof decreased after the original heat of solutionnoted in the first minute as shown below, thereby indicating that thefast hydrating =Form II anhydrous sodium tripolyphosphate had beenconverted into the slow hydrating variety by the heat treatment.

Time (minutes): Temperature of slurry F.)

4 Example 2 A lot of Form 11 anhydrous sodium tripolyphosphate asreceived from the supplier was divided into four portions. 75 grams ofone portion was added to 100 cc. of

water containing 25 grams of anhydrous sodium sulfate and having atemperature of 170 F. in accordance with the above test procedure.During the next 15 minutes the slurry thickened and the temperaturethereof rose as shown below, thereby indicating that thetripolyphosphate was a fast hydrating variety.

Time (minutes): Temperature of slurry F.) O 170 1 172.5 2 172.5 3 173 4174.5 5 176 6 177.5 7 179 8 180 9 181 10 182 11 182.5 12 183 13 183 14183 15 184 One hundred grams each of the other three port1ons werespread evenly in six inch moisture dishes and ovendried at 100 C. for 6hours, at 100 C. for 16 hours, and at 380 C. for 1 hour respectively.Each of the three portions was then packed hot into separate dry Masonjars and allowed to cool to room temperature. grams of each of thesethree heat-treated portions was separately added to cc. of watercontaining 25 grams of anhydrous sodium sulfate and having a temperatureof 4.0 170 F. in accordance with the above test procedure. During thenext 15 minutes each of the three slurries remained thin and thetemperatures thereof decreased after the original heat of solution notedin the first minute as shown below, thereby indicating that the fasthydrating Form II anhydrous sodium tripolyphosphate had been convertedinto the slow hydrating variety by each of these three heat treatments.

50 'lripolyphosphate Heat Treatment Time (minutes) 6 hours 16 hours 1hour at at7100 C. at100 0. 320 C,

Temperature of Slurry F.)

Example 3 Two samples of an aqueous slurry of the following typicaldetergent composition (calculated on a powder basis) having an overallwater content of 40% were agitated in a crutcher for 45 minutes at atemperature 75 of 160 F.

Sodium silicate (Na OzSio of 1:2.0) 6.0 Sodium carboxymethylcellulose0.5 Water 7.0 Sodium sulfate 20.0 Miscellaneous impurities 3.3

Total 100.0

One of these two samples (Formula A) contained fast hydrating Form IIanhydrous sodium tripolyphosphate as received from the supplier. Theother sample (Formula B) contained sodium tripolyphosphate from the samelot as that in Formula A. However, the sodium tripolyphosphate inFormula B was tray-dried for 17 hours at 110 C. and then cooled to roomtemperature before addition to Formula B. Just prior to spraying, aportion from the slurries of Formula A and Formula B was separatelyquenched in hot ethyl alcohol to arrest further hydration. Theseportions were examined by means of X-ray diffraction patterns todetermine the percent of tripolyphosphate which had hydrated to thehexahydrate. Other portions of the slurry were removed and theviscosities and pH values of 1% solutions were measured. These data arepresented below.

Percent Sodium Viscosity of Formula TripolypH Slurry phosphate HydrationA 100 9. 95 thick. B 10.0 moderately thin.

Sodium Tri- Silica Formula polyphosphate pH Floo Decomposition A lav-2n9. 4 large. B slip-hi- 9. 7 slight.

From an examination of the above data the following beneficial resultsflowing from the process of the invention will be readily apparent. Theamount of sodium tripolyphosphate Which was hydrated into thehexahydrate in Formula A containing the fast hydrating Form II anhydroussodium tripolyphosphate as received from the manufacturer was remarkablyhigher (100% hydration) than was true in Formula B which contained slowhydrating Form II anhydrous sodium tripolyphosphate (10% hydration). Thedata also show that the viscosity of the aqueous crutcher slurry ofFormula A increased until it became thick due to the presence of a largeamount of hexahydrate, while the viscosity of the crutcher slurry ofFormula B did not change appreciably during crutching, but remainedmoderately thin and easy to handle. It will also be noted that the pH ofFormula A changed from 9.95 to 9.4 (a change of 0.5) from the time ofcrutching to the time when the spray-dried product was redissolved inwater as compared with a pH change from 10.0 to 9.7 (a decrease of only0.3) for Formula B during the same interval. The spray-dried product ofFormula A was also undesirable in that an aqueous solution thereofcontained a large amount of silica floc and hence was quite turbid ascontrasted with an aqueous solution of the spray-dried product ofFormula B which had only a slight amount of silica floc and hence wouldnot be unsightly to the consumer. In addition, the spray-dried productof Formula A contained a large amount of decomposition products (pyroandorthophosphates) of the tripolyphosphate, while the spray-dried productof Formula B employing the slow hydrating variety of Form II anhydroussodium tripolyphosphate produced in accordance with the process of theinvention contained only a slight amount of decomposition products.

It will be appreciated that various modifications and changes may bemade in the process set forth herein without departing from the spiritthereof and accordingly the process is to be limited only Within thescope of the appended claims.

I claim:

1. The process of converting fast hydrating Form II anhydrous sodiumtripolyphosphate into slow hydrating Form II anhydrous sodiumtripolyphosphate comprising heating the solid fast hydrating Form IIanhydrous sodium tripolyphosphate alone at a temperature of from about100 C. to about 380 C. for a time of from at least about 6 hours to atleast about 1 hour respectively to remove the adsorbed water; said fasthydrating Form II anhydrous sodium tripolyphosphate being characterizedby the fact that a stirred aqueous slurry thereof consisting of 100parts of water, 25 parts of anhydrous sodium sulfate, and parts of saidfast hydrating phosphate at an initial temperature of 170 F. willthicken and the temperature will rise during standing for 15 minutes andsaid slow hydrating Form II anhydrous sodium tripolyphosphate beingcharacterized by the fact that a stirred aqueous slurry thereofconsisting of parts water, 25 parts of anhydrous sodium sulfate, and 75parts of said slow hydrating phosphate at an initial temperature of F.will remain thin and the temperature will fall during standing for 15minutes.

2. The process as set forth in claim 1 comprising heating the solid fasthydrating Form II anhydrous sodium tripolyphosphate alone at atemperature of about 100 C. for at least about 6 hours to remove theadsorbed water.

3. The process as set forth in claim 1 comprising heating the solid fasthydrating Form II anhydrous sodium tripolyphosphate alone at atemperature of about 380 C. for at least about 1 hour to remove theadsorbed water.

References Cited in the file of this patent UNITED STATES PATENTS2,622,068 Hizer Dec. 16, 1952 2,920,939 Edwards Jan. 12, 1960 FOREIGNPATENTS 680,346 Great Britain Oct. 1, 1952 OTHER REFERENCES T. Anorg.Allgern. Chem., Sodium Polyphosphates, Andress et al., 237, pages113-131, 1938.

1. THE PROCESS OF CONVERTING FAST HYDRATING FORM 11 ANHYDROUS SODIUMTRIPOLYPHOSPHATE INTO SLOW HYDRATING FORM 11 ANHYDROUS SODIUMTRIPOLYPHOSPHATE COMPRISING HEATING THE SOLID FAST HYDRATING FROM 11ANHYDROUS SODIUM TRIPOLYPHOSPHATE ALONE AT A TEMPERATURE OF FROM ABOUT100*C. TO ABOUT 380*C. FOR A TIME OF FROM AT LEAST ABOUT 6 HOURS TO ATLEAST ABOUT 1 HOUR RESPECTIVELY TO REMOVE THE ADSORBED WATER; SAID FASTHYDRATING FROM 11 ANHYDROUS SODIUM TRIPOLYPHOSPHATE BEING CHARACTERIZEDBY THE FACT THAT A STIRRED AQUEOUS SLURRY THEREOF CONSISTING OF 100PARTS OF WATER, 25 PARTS OF ANHYDROUS SODIUM SULFATE, AND 75 PARTS OFSAID FAST HYDRATING PHOSPHATE AT AN INITIAL TEMPERATURE OF 170*F. WILLTHICKEN AND THE TEMPERATURE WILL RISE DURING STANDING FOR 15 MINUTES ANDSAID SLOW HYDRATING FORM 11 ANHYDROUS SODIUM TRIPOLYPHOSPHATE BEINGCHARACTERIZED BY THE FACT THAT A STIRRED AQUEOUS SLURRY THEREOFCONSISTING OF 100 PARTS WATER, 25 PARTS OF ANHYDROUS SODIUM SULFATE, AND75 PARTS OF SAID SLOW HYDRATING PHOSPHATE AT AN INITIAL TEMPERATURE OF170*F. WILL REMAIN THIN AND THE TEMPERATURE WILL FALL DURING STANDINGFOR 15 MINUTES.